More specifically, the present invention relates to means of managing the volume of a water reserve capable of being supplied for example, but not exclusively, by natural rainfall.
Even more specifically, the present invention applies quite particularly, but not exclusively, to the management of the volume of the water reserve contained in plant growing trays, for example for roofs of buildings or equivalent, such as for example the trays described in the document EP 1 044 599.
In EP 1 044 599 are described trays formed preferably of plastic material and including:                a bottom of general rectangular shape,        a lateral edge which surrounds the bottom,        a plurality of recesses or compartments formed in the bottom,        means which enable a fluidic communication between the different recesses or compartments, for example formed of troughs on the top of the partitions delimiting the recesses and,        overflow orifices on the top of said partitions.        
Trays of the aforementioned type have already known great success. However, they are sometimes subject to suddenly receiving a very considerable volume of water, in the event for example of a storm. It is advisable as far as possible to discharge this important input at least in part quite quickly for the comfort of the cultivated plants and to make the storage volume again available for following storms, while making it possible to maintain a contrario a consequent reserve useful in the event of a long drought period.
In this context the aim of the present invention is to perfect the prior art.